Shelf unit



FIG. 1 is a perspective view of a shelf unit showing our new design;

FIG. 2 is a right side elevational view thereof, the left side elevational view thereof being identical;

FIG. 3 is a top plan view thereof;

FIG. 4 is a front elevational view thereof; and

FIG. 5 is a rear elevational view thereof. 

The ornamental design for a shelf unit, substantially as shown and described. 